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Chapter I2
Section 1 Water in the Air
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What causes wind?
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Chapter I2
Section 1 Water in the Air
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How do clouds form?
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Chapter I2
Section 1 Water in the Air
Do now?
If a cold air mass meets a warm air mass
full of moist air, the cold air will sink and
push the warm air upwards. When this
happens, energy will be removed from the
warm air. As the energy is removed, what
will happen to the water in the air?
Write your answers in your science journal.
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Chapter I2
Section 1 Water in the Air
Objectives
1. Describe how relative humidity is affected by
temperature and levels of water
vapor.
2. List three types of cloud forms.
3. Identify the four kinds of air masses that
influence weather in the United
States.
4. Describe the four major types of fronts.
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Agenda
• Today we will:
– Learn about weather by reading, discussion and
investigation
– Do now
– Notes
– Reading
– Exit ticket
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Vocabulary
•
•
•
•
•
Section 1 Water in the Air
weather
humidity
cloud
air mass
front
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Chapter I2
Section 1 Water in the Air
The Water Cycle
• The condition of the atmosphere is affected by the
amount of water in the air. Water in liquid, solid, and
gaseous states is constantly being recycled through
the water cycle.
• The water cycle is the continuous movement of
water from sources on Earth’s surface into the air,
onto and over land, into the ground, and back to the
surface.
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Chapter I2
Section 1 Water in the Air
Humidity
• Humidity is the amount of water vapor in the air.
• The air’s ability to hold water vapor changes as the
temperature of the air changes.
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Chapter I2
Section 1 Water in the Air
Condensation
• Condensation is the process by which a gas,
such as water vapor, becomes a liquid.
• Dew Point The dew point is the temperature at
which a gas condenses into a liquid.
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Chapter I2
Section 1 Water in the Air
Clouds
• A cloud is a collection of small water droplets or
ice crystals suspended in the air, which forms
when the air is cooled and condensation occurs.
• Clouds are classified by form, and by altitude.
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Chapter I2
Section 1 Water in the Air
Clouds, continued
• Cumulus Clouds are puffy, white clouds that
tend to have flat bottoms.
• Stratus Clouds are clouds that form in layers.
• Cirrus Clouds are thin, feathery, white clouds
found at high altitudes.
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Chapter I2
Section 1 Water in the Air
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Chapter I2
Section 1 Water in the Air
Clouds, continued
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Chapter I2
Section 1 Water in the Air
Precipitation
• Rain is the most common form of precipitation.
• Sleet and Snow Sleet forms when rain falls
through a layer of freezing air. Snow forms when
temperatures are so cold that water vapor changes
directly to a solid.
• Hail are balls or lumps of ice that fall from clouds.
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Chapter I2
Section 1 Water in the Air
Formation of Clouds and Precipitation
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Visual Concept
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the Esc key.
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Chapter I2
Section 2 Air Masses and Fronts
Air Masses
• Changes in weather are caused by the movement
and interaction of air masses.
• An air mass is a large body of air where temperature
and moisture content are constant throughout.
• Cold Air Masses Most of the cold winter weather in
the United States is influenced by three polar air
masses.
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Chapter I2
Section 2 Air Masses and Fronts
Air Masses, continued
• Warm Air Masses Four warm air masses influence
the weather in the United States.
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Chapter I2
Section 2 Air Masses and Fronts
Fronts
• The area in which two types of air masses meet is
called a front.
• Cold Fronts A cold front forms where cold air
moves under warm air,which is less dense, and
pushes the warm air up.
• Warm Fronts A warm front forms where warm air
moves over cold, denser air.
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Chapter I2
Section 2 Air Masses and Fronts
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Chapter I2
Section 2 Air Masses and Fronts
Fronts, continued
• Occluded Front An occluded front forms when a
warm air mass is caught between two colder air
masses. An occluded front has cool temperatures and
large amounts of rain and snow.
• Stationary Front A stationary front forms when a
cold air mass meets a warm air mass. A stationary
front often brings many days of cloudy, wet weather.
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Chapter I2
Section 2 Air Masses and Fronts
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Chapter I2
Section 3 Severe Weather
Thunderstorms
• Lightning is an electric discharge that occurs
between a positively charged area and a negatively
charged area. Thunderstorms are very active
electrically.
• Thunder is the sound that results from the rapid
expansion of air along the lightning strike.
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Chapter I2
Section 3 Severe Weather
Lightning and Thunder
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Visual Concept
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Chapter I2
Section 3 Severe Weather
Tornadoes
• A tornado is a small, spinning column of air that has
high wind speeds and low central pressure and that
touches the ground.
• A tornado starts out as a funnel cloud that pokes
through the bottom of a cumulonimbus cloud and
hangs in the air. The funnel cloud becomes a tornado
when it makes contact with Earth’s surface.
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Chapter I2
Section 3 Severe Weather
Tornadoes, continued
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Chapter I2
Section 3 Severe Weather
Hurricanes
• How a Hurricane Forms A hurricane begins as a
group of thunderstorms moving over tropical ocean
waters. Winds traveling in two different directions
meet and cause the storm to spin.
• Damage Caused by Hurricanes Hurricanes can
cause a lot of damage when they move near or onto
land. Wind speeds of most hurricanes range from
120 to 150 km/h.
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Chapter I2
Section 3 Severe Weather
Hurricanes, continued
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Exit Ticket
• What are fronts and air masses and how
do they influence weather?
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